1. Technical Field
This invention relates to on-demand printers printing U.P.C./EAN bar-codes and, more particularly, to a method and associated apparatus for printing a pre-defined symbology character set as a series of bars separated by spaces in which the bars are formed of horizontal rows of close adjacent dots while preventing ambiguous decoding of similar character pairs in which one character employs wide bars and one character employs narrow bars in which the method comprises the steps of, subtracting at least a portion of one dot or more per horizontal row from bars of similar characters employing narrow bars; and, adding at least a portion of one dot or more per horizontal row to bars of similar characters employing wide bars.
2. Background Art
U.P.C./EAN symbology is employed in marking products found in supermarkets and the like which are scanned by an optical reader connected to a pricing and inventory computer system. While for the most part a fault-tolerant system in which it is virtually impossible for a label to be misread as a valid identification number for another product, there is one big problem with the U.P.C./EAN symbology--ambiguity with the decode of the 1 & 7 and the 2 & 8 symbol characters. The problem can be understood from the U.P.C./EAN symbology character set as depicted in FIG. 1 taken with FIG. 2, which depicts the 1 and 7 characters. Due to the manner in which the characters are decoded, unless there is a clear distinction as to the bar sizes and spacing, both characters can be decoded as a "T=4,4" character. To achieve a scanable distinction between the 1, 2, 7, and 8 characters, these characters typically have slightly different dimensions by about 8% from the other characters (i.e. 0, 3, 4, 5, 6, and 9). The original specification required that film master based symbols, capable of resolution in excess of 10,000 dots per inch (dpi), precisely add the printing compensation required.
Original tolerances precluded any matrix demand printing platform printing U.P.C./EAN symbology from performing the correction. Consequently, the print quality measurements for these symbols always lagged web symbols. The newly published specification (September 1994) allows for a new method of measurement which includes this correction; but, it has been assumed to be impossible to successfully implement it on demand platforms. It turns out that the new method, called "decodability", does not penalize print quality measurements for slight over-compensation of the ambiguous correction. Therefore, high resolution printing platforms, such as thermal demand printers with resolution on the order of 300 dpi or more, are capable of printing higher quality symbols with the adjusted font than any printing platform currently on the market or described in the art. What is needed is a way to use the new specification to advantage without having to procure expensive media or print at slow speeds to insure a high enough print quality that still passes specification after the decodability penalty is assessed.
Solving this problem in demand printers is not new in and of itself. The first demand printers for U.P.C. symbology had 10,000 dpi resolution elements (the same as film master based symbols) and, therefore, were able to print on demand with the same quality and resolution. One such printer was the model 8312 manufactured by Interface Mechanisms, Inc. (now known as Intermec, Inc., the assignee of the present invention). No other demand printing process has ever been able to print in-specification U.P.C./EAN symbols and have resorted to printing higher than necessary quality symbols to compensate and, hence, carried a higher cost.
The principal disadvantages of prior art approaches to solving this problem in on-demand printers are the higher cost and slower speed. Most demand processes are extremely cost sensitive and frequently borderline symbols are produced which, consequently, pass all parameters except decodability. Retail systems for reading and processing U.P.C./EAN symbols often keep accurate records of how many symbols are misread and how many codes must be hand keyed in by employees as a result of a failure to successfully read the symbols. The data are associated with the vendors who supplied the products. And, vendors have been subject to fines of up to $5,000 per infraction for supplying products with U.P.C./EAN symbols which are not decodable. Thus, in many cases, vendors have been forced to resort to expensive pre-printing processes in order to avoid the lack of quality of demand printing platforms.
Wherefore, it is an object of the present invention to provide an on-demand printer in which U.P.C./EAN symbols can be printed the same way as any other bar code symbology font and achieve the same performance levels.
It is another object of the present invention to provide an on-demand printer in which U.P.C./EAN symbols can be printed with low-cost consumables, higher throughput, and a lower likelihood of penalty fines.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing figures which accompany it.